This invention relates to the thermoforming molds for the heat-promoted application of a covering on a plastics product formed by said molds and for the trimming, on completion of said application, of said product along at least a portion of its perimeter.
The molds of this type comprise a male element whereon a heated sheet constituting the product to be covered is disposed, and means to spread said covering material on the sheet disposed on the male element, and a female element adapted to be pressed against said male element while said sheet to be covered and said covering material thereon are interposed therebetween. Arranged on at least a portion of the perimeter of said male element there are trimming knives which are movable transversely to said male element and are adapted to cut both said product and its covering along pre-established edges and when said mold is closed.
The molds of the type described above may be used with any material to be covered and any covering material. The material to be covered may be formed of a sheet of any substantially rigid and heat-formable (i.e., thermoplastic) material, e.g. polyolefines, or acrylonitrile, butadiene and styrene copolymers, possibly containing any filling organic or inorganic material. In particular, the material to be covered may be formed of polyolefines filled with cellulose fibers, e.g. sawdust, as described in the German Pat. No. 2.412.538 published on Oct. 31, 1974. The product to be covered may present any shape and peripheral outline, and it may be intended for any purpose or use. In particular, the mold according to the invention may be used for manufacturing internal upholstery panels for motor vehicles or any other similar panels, having an at least slightly concave and/or convex configuration. The covering material may be formed of any material which is compatible with the product to be covered and which may be secured, specifically heat-secured, thereto. In particular, the covering material may be formed of plastics sheets, e.g. PVC, textile cloths, woven or non-woven or knitted fabrics either of natural and/or synthetic fibers, which may be plasticized, specifically, with vinyl resins.
In the heretofore known molds of the type mentioned above, the product is trimmed at a preferably rounded corner or at a curved connection between two substantially rectilinear sides of the outline of said product, by means of corresponding curved and complementary end portions of two side knives associated with said rectilinear sides. However, the disadvantage of this system is that in the opened position of said knives associated with the two substantially rectilinear sides of the outline of said product, an interstice is formed between the adjacent and co-operating ends of said knives, in the opened condition thereof, at the corner or radiused corner between said rectilinear sides, and that the covering material may find its way thereinto and be pinched and squeezed between the co-operating ends of said knives when they close, i.e., when they move toward the respective rectilinear sides of the outline of the product, thus forming undesired laps or tabs at the corner or radius between said rectilinear sides.
The invention aims to eliminate this disadvantage and, to achieve this object, it is characterized in that--at least at a preferably rounded corner or curved radius between two rectilinear or substantially rectilinear sides of the outline of the product--a knife, shaped correspondingly to said corner or radius and comprising end portions slidably engaging outer planar surfaces of pointed or tapered end extensions of said side knives, is arranged between the side knives associated with said rectilinear sides, means being provided to move simultaneously the side knives and interposed knife, while the sliding surfaces between the extensions of the side knives and interposed shaped knife are at such an angle to the directions of movement of the two side knives and interposed shaped knife as to constantly keep in contact with each other during the movement of said knives.
It is now apparent that in this embodiment of the mold, no interstice is formed at the corner or radius between two substantially rectilinear portions of the outline of said product when the trimming knives are opened, i.e., retracted from the male element of the mold, because between the two side knives associated with said rectilinear sides there is arranged the shaped knife associated with said corner or radius. By extending the shaped knife behind the tapered end extensions of the two side knives and by slidingly associating said shaped knife and said extensions of the two side knives along contacting surfaces at an angle to the direction of movement of the knives, there is avoided the formation of open interstices between the two side knives and interposed shaped knife. Therefore, the covering material cannot be pinched between the trimming knives when they close against the male element of the mold.
Preferably, according to a further characteristic of the invention, which may be used alone or in combination with the characteristics set forth above, the trimming knives are movable in planes that are inclined to the surface of the covered product, and usually inclined upwardly towards the inner region of the male element of the mold, at an angle of about 0.degree. to 15.degree. to the horizontal, so as to fold the covering material on the trimmed edge of the underlying product, i.e. to cover said trimmed edge of the product at least partially with covering material. By this arrangement, the trimmed adges of the covered product will be completely finished and the product is ready to be used with no further finishing or covering of its edges.